A very general doorway to "strange constructs": Perl Data Structures Cookbook; see in particular HASHES OF ARRAYS.

  $text->{$line}[$pos - 1] = $word;
       ^ ^      ^
       | |      |
       | hash   |
dereference    array
[download]

I used $pos - 1 as positions start from 1, but array indices start from 0.

Note that the bracket types are the same as when creating the data:

$VAR1 = {
          'c3' => [
                    'Phasellus',
                    'non',
                    'erat'
                  ],
          'b2' => [
                    'consectetuer',
                    'adipiscing',
                    'elit.'
                  ],
          'a1' => [
                    'Lorem',
                    'ipsum',
                    'dolor',
                    'sit',
                    'amet,'
                  ]
        };
[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Thank you very much for the links and for the fish as well. If i can, what about the original order of the text? a1->b2->c3? Unfortunately, since the lines are indexed in a more complicated fashion than the one I reported, I cannot simply sort hash keys. In fact the original order is governed by Postgres only.

the original order is governed by Postgres only

That is a very bad design. See the documentation:

If sorting is not chosen, the rows will be returned in an unspecified order. The actual order in that case will depend on the scan and join plan types and the order on disk, but it must not be relied on. A particular output ordering can only be guaranteed if the sort step is explicitly chosen.

If you don't want to build a hash, use an array.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]